Move login command warning

This commit moves where the warning is for the login command so that it
only displays when the command is invoked, and not when the plugin is
loaded.

lib/vagrant/cli.rb

@@ -23,6 +23,10 @@ module Vagrant
         return 0
       end
 
+      if @sub_command == "login"
+        $stderr.puts "WARNING: This command has been deprecated and aliased to `vagrant cloud auth login`"
+      end
+
       # If we reached this far then we must have a subcommand. If not,
       # then we also just print the help and exit.
       command_plugin = nil

plugins/commands/login/plugin.rb

@@ -14,7 +14,6 @@ module VagrantPlugins
       command(:login) do
         require File.expand_path("../../cloud/auth/login", __FILE__)
         init!
-        $stderr.puts "WARNING: This command has been deprecated in favor of `vagrant cloud auth login`"
         VagrantPlugins::CloudCommand::AuthCommand::Command::Login
       end